Method and system for reducing arterial restenosis in the presence of an intravascular stent

ABSTRACT

A first electrode is positioned within an artery proximate an implanted intravascular stent. A second electrode is positioned at a separate location relative the position of the first electrode. Electrical energy is then delivered between the first and the second electrodes to produce an electrical field adjacent the implanted intravascular stent. When a intravascular stent is implanted in a coronary artery, the delivery of the electrical energy is coordinated to cardiac cycles detected in sensed cardiac signals, where the delivery of the electrical energy between the first electrode and the second electrode occurs during a predetermined portion of the cardiac cycle.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a division of U.S. patent application Ser. No.09/294,724, filed on Apr. 19, 1999, the specification of which isincorporated herein by reference.

FIELD OF THE INVENTION

The present subject matter relates generally to medical devices and moreparticularly to a method and system for producing an electric fieldadjacent an intravascular stent.

BACKGROUND OF THE ART

The normal human heart is a strong, muscular pump a little larger than afist. It pumps blood continuously through the circulatory system. Eachday the average heart “beats” (or expands and contracts) 100,000 timesand pumps about 2,000 gallons of blood. In a 70-year lifetime, anaverage human heart beats more than 2.5 billion times.

The heart pumps blood through a circulatory system, which is a networkof elastic tubes through which blood flows as it carries oxygen andnutrients to all parts of the body. The circulatory system includes theheart, lungs, arteries, arterioles (small arteries), and capillaries(minute blood vessels). It also includes venules (small veins) andveins, the blood vessels through which blood flows as it returns to theheart.

The circulating blood brings oxygen and nutrients to all the organs andtissues of the body, including the heart itself. The blood also picks upwaste products from the body's cells. These waste products are removedas they're filtered through the kidneys, liver and lungs.

Over time, the coronary arteries which supply the heart muscle withblood can become clogged. One cause of clogged arteries is due to acondition called atherosclerosis, or hardening of the arteries.Atherosclerosis causes a constriction of the inner lumen of the affectedartery when the lumen of the arteries become more narrow due to apathological accumulation of cells, fats and cholesterol called plaque.The descriptive term given to this narrowing of the coronary arteries is“stenosis.” Stenosis means constriction or narrowing. A coronary arterythat is constricted or narrowed is referred to as stenosed. Whenstenosis of the coronary artery is sufficient to deprive the heartmuscle of the oxygen levels necessary for cell viability, the result istypically myocardial infarction, typically referred to as a heartattack.

A heart attack occurs when the blood supply to part of the heart muscleitself, the myocardium, ceases or is severely reduced. This occurs whenone or more of the arteries supplying blood to the heart muscle(coronary arteries) becomes partially or completely obstructed by plaquestenoses. If cessation of the blood supply occurs for a long time, heartmuscle cells suffer irreversible injury and die. Severe disability ordeath can result, depending on how much heart muscle is damaged.

Coronary artery bypass surgery is a heart operation used to treatcoronary artery disease. In coronary artery bypass surgery a bloodvessel is used to go around or “bypass” clogged coronary (heart)arteries. During the “bypass” procedure, a blood vessel from thepatient's chest or leg is used as the “bypass” conduit. For venous“bypass” grafts, one end of the vessel is attached to the aorta (thelarge artery coming out of the heart) and the other end is attached tothe coronary artery below the point where it's clogged. Once the cloghas been bypassed, blood can once again flow through the bypass graft tothe heart, in a manner that prevents ischemia and infarction. Almosthalf a million coronary bypass operations are performed each year in theUSA.

Another procedure for opening clogged coronary arteries is to performpercutaneous transluminal coronary angioplasty, or balloon angioplasty.Balloon angioplasty is an established and effective therapy for somepatients with coronary artery disease. Balloon angioplasty is used todilate (widen) arteries narrowed by plaque. During the procedure, acatheter with a deflated balloon on its tip is passed into the narrowedpart of the artery. The balloon in then inflated, and the narrowed areais widened. Balloon angioplasty is a less traumatic and less expensivealternative to bypass surgery for some patients with coronary arterydisease. However, in 25 to 30 percent of patients the dilated segment ofthe artery renarrows (restenosis) within six months after the procedure.The patient may then require either to repeat the balloon angioplasty orto undergo coronary bypass surgery.

One approach to preventing restenosis has been to insert a “stent”across the stenosed area of coronary artery. A stent is a metallic wiremesh tube that is used to prop open an artery that has been recentlydilated using balloon angioplasty. The stent is collapsed to a smalldiameter, placed over an angioplasty balloon catheter and moved into thearea of the blockage. When the balloon is inflated, the stent expands,locking in place to form a rigid support (structural scaffolding) whichholds the artery lumen open. The stent remains in the artery permanentlyto help improve blood flow to the heart muscle. However, reclosure(restenosis) remains an important issue with the stent procedure.

Several approaches have been taken to reduce the occurrence ofrestenosis associated with the stent procedure. Stents have beenimpregnated with drugs and chemicals that emit radiation (gamma-rays) inan attempt to reduce the frequency of restenosis. Also, drug elutingstents have been used in an attempt to reduce the occurrence ofrestenosis. However, a need still exists for additional safe andeffective treatments to prevent restenosis after the placement of anintravascular stent.

SUMMARY OF THE INVENTION

The present subject matter provides a method and a system for producingelectrical energy adjacent an intravascular stent. The electrical energy(or current density) supplied to the artery surrounding the stent issufficient to structurally modify, damage and/or kill cells within theartery. By effecting the cells of the artery surrounding the stent, itis believed that the occurrence of restenosis associated with the stentprocedure will be reduced.

The present subject matter includes a system and method for positioninga first electrode within the vasculature proximate an implanted stent,where the stent is electrically conductive. A second electrode is thenpositioned at a remote position relative to the first electrode. In oneembodiment, the remote position is on the dermal surface of the patient.Cardiac signals are then sensed from the patient. The cardiac signalsinclude cardiac cycles which indicate the electrical events of cardiacexcitation. Electrical energy is then delivered between the firstelectrode and the second electrode during a predetermined portion of asensed cardiac cycle.

In one embodiment, the first electrode is positioned on a transvenouscatheter. The transvenous catheter includes a first lead conductor whichis contained within the elongate body of the transvenous catheter andserves to couple the first electrode to the first lead connector. In anadditional embodiment, the second electrode is coupled to an externallead. The external lead includes an elongate body and a second leadconductor contained within the elongate body that couples the secondelectrode to a second lead connector.

The transvenous catheter allows at least a portion of the firstelectrode to be positioned within the lumen of the implanted stent.Alternatively, the first electrode is positioned entirely within thelumen of the implanted stent. In one embodiment, first electrode ispositioned within the lumen of the stent in such a manner that the firstand second electrode ends of the first electrode align with the firstand second stent ends of the implanted stent, respectively. In oneembodiment, the length of the first electrode is between 80 and 120% ofthe predetermined length of the intravascular stent.

In one embodiment, the first and second electrodes are coupled to apulse generator. In one embodiment, the pulse generator includes aprogramming circuit coupled to a display screen, where the programmingcircuit is used to control the display screen to request parametervalues for the electrical energy pulse The pulse generator furtherincludes a data input device which is coupled to the programming circuitand the display screen. The programming circuit can then receiveparameter values for the electrical pulses through the data inputdevice. In one embodiment, the data input device is an alphanumerickeyboard.

In one embodiment, the first and second electrodes are releasablycoupled to the pulse generator through a first input/output socket and asecond input/output socket, respectively. In one embodiment, cardiacsignals are sensed between the first and second electrodes and thecardiac signals are provided to an electrogram analysis circuit. In oneembodiment, the electrogram analysis circuit detects cardiac complexesin the sensed cardiac signal. A microprocessor is additionally coupledto the programming circuit, the electrogram analysis circuit and anenergy source. The microprocessor receives the parameter values from theprogramming circuit and the cardiac complexes in the sensed cardiacsignal from the electrogram analysis circuit. The microprocessor alsocontrols the energy source to generate the electrical energy pulsehaving the parameter values for the intravascular stent when apredetermined portion of a cardiac complex occurs in the cardiac signal.

In an additional embodiment, two or more surface electrocardiogramelectrodes are coupled to the pulse generator. The electrogram analysiscircuit is adapted to receive one or more cardiac signals (includingcardiac complexes) sensed between the two or more surfaceelectrocardiogram electrodes. The microprocessor then controls theenergy source to generate the electrical energy pulse having theparameter values for the intravascular stent when a predeterminedportion of a cardiac complex occurs in the cardiac signal sensed betweenthe two or more surface electrocardiogram electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a system according to one embodiment of thepresent subject matter;

FIG. 2 is a block diagram of a pulse generator according to oneembodiment of the present subject matter;

FIG. 3 is a schematic of a catheter according to one embodiment of thepresent subject matter;

FIG. 4 is a schematic of a catheter according to one embodiment of thepresent subject matter;

FIG. 5 is a flow chart illustrating one embodiment of the presentsubject matter;

FIG. 6 is a flow chart illustrating one embodiment of the presentsubject matter;

FIG. 7 is a flow chart illustrating one embodiment of the presentsubject matter; and

FIG. 8 is a schematic of a catheter according to one embodiment of thepresent subject matter.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof and in which is shown byway of illustration specific embodiments in which the invention can bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to practice and use the invention, andit is to be understood that other embodiments may be utilized and thatelectrical, logical, and structural changes may be made withoutdeparting from the spirit and scope of the present invention. Thefollowing detailed description is, therefore, not to be taken in alimiting sense and the scope of the present invention is defined by theappended claims and their equivalents.

Restenosis of arteries after balloon angioplasty continues to be aserious problem. Restenosis has even been found to be a problem afterthe placement of an intravascular stent which is designed to hold anartery open after balloon angioplasty. The present subject matteraddresses the problem of restenosis associated with the stent procedureby providing electrical energy to the artery tissues surrounding thestent. The electrical energy (or current density) supplied to the arterysurrounding a stent is sufficient to structurally modify, damage and/orkill cells within the artery.

The general structure of an artery has three layers. The first layerconsists of a single continuous layer of endothelial cells along thelumen of the artery. The endothelial cells attach to a second layer,which is a muscular middle layer. This second layer is referred to asthe tunica media. The muscular middle layer consists principally ofmuscular tissue (smooth muscle cells) which are arranged in lamellae anddisposed circularly around the vessel. The thickness of the artery wallis due in large part to this muscular middle layer. The third layer isthe outer most layer and is referred to as the tunica adventitia. Thethird layer consists mainly of fine and closely felted bundles ofconnective tissue and elastic fibers.

An electrical field is localized to the arterial tissue surrounding thestent. In one embodiment, the electrical field is produced in tissuesadjacent to the stented region of an artery by effecting a voltagedifference between a first electrode positioned adjacent the stent and asecond electrode positioned at a remote position relative to the firstelectrode. The electrical energy is supplied from a capacitor whichcreates a potential difference (voltage) between the first electrode andthe second electrode. The potential difference results in creation of anelectric field having a space-varying and time-varying intensity thatcan be expressed as current density. In one embodiment, the strength ofthe electrical energy is sufficient to irreparably damage the cellswithin the structure of the artery, where the cells most heavily damagedare the smooth muscle cells located in the medial layer of the artery.However, the electrical energy is not sufficiently strong to causesignificant modification of adjacent myocardial tissue, thereby leavingthe remaining cardiac tissue unaffected by the electrical energy.

Referring now to FIG. 1, there is shown a system 100 according to oneembodiment of the present subject matter. The system 100 anintravascular stent 102, where the intravascular stent 102 in oneembodiment is made of metal. The system 100 further includes a firstelectrode 104, where the first electrode 104 is positioned on a catheter108 and is coupled to a first lead connector 110 through a first leadconductor (not shown). Additionally, the system 100 includes a secondelectrode 112, the second electrode 112 positioned on an external lead114 and is coupled to a second lead connector 116 through a second leadconductor (not shown).

The catheter 108 includes an elongate body 118 having a peripheralsurface 120, a proximal end 122, and a distal end 124. The firstelectrode 104 is positioned on the peripheral surface 120 of thecatheter 108 between the proximal end 122 and the distal end 124. Afirst lead conductor (not shown) is contained within the elongate body118 and couples the first electrode 104 to the first lead connector 110and the proximal end 122. The catheter 108 further includes a guidewirelumen (not shown) which extends through at least a portion of theelongate body 118. In an alternative embodiment, the elongate body 118is adapted to allow the guidewire to extend through the entire length ofthe elongate body 118.

The external lead 114 includes an elongate body 130 having a peripheralsurface 132, a proximal end 134, and a distal end 136. The secondelectrode 112 is positioned, or attached, at the distal end 136 of theexternal lead 114. A second lead conductor (not shown) is containedwithin the elongate body 130 and couples the second electrode 112 to thesecond lead connector 116 at the proximal end 134 of the elongate body130. In one embodiment, the second electrode 112 is a patch electrodewhich is constructed of a conductive gel overlying a metallic foil, asare known.

The system 100 further includes a pulse generator 140. The pulsegenerator 140 includes a programming circuit (not shown) and a displayscreen 144. The programming circuit is coupled to and controls thedisplay screen 144 to request values for an electrical pulse to beentered into the pulse generator 140. A data input device is coupled tothe programming circuit and display screen 144. The data input devicereceives the parameter values for the electrical pulse and displays thevalues on the display screen 144. In one embodiment, the data inputdevice is a keyboard 146. Alternatively, the data input device is atouch sensitive layer (not shown) integrated into the display screen 144which allow for data input by touching predetermined regions of thelayer. Additionally, a computer mouse 148 can be used to supplyparameter values, along with other information, by responding to andinputting information presented on the display screen 144.

The pulse generator 140 further includes a first input/output socket 150and a second input/output socket 152. The first and second input/outputsockets 150 and 152 are coupled to an electrogram analysis circuit (notshown) housed within the pulse generator 140. The first lead connector110 and the second lead connector 116 releasably couple to the first andsecond input/output sockets 150 and 152, which allows for electricalsignals to be sensed between the first and second electrodes, 104 and112. In one embodiment, the electrogram analysis circuit includes signalamplifiers to amplify the electrical signals sensed between the firstand second electrodes 104 and 112.

In one embodiment, the electrical signals sensed between the first andsecond electrodes 104 and 112 are cardiac signals. The electrogramanalysis circuit receives the sensed cardiac signals and analyzes thecardiac signal to detect the occurrence of cardiac complexes in thesensed cardiac signal. In one embodiment, the electrogram analysiscircuit detects the occurrence of the QRS-complex of the cardiaccomplex. Alternatively, the electrogram analysis circuit detects otherknown portions of the cardiac complex, such as the occurrence of T-wavesor the occurrence of the complete cardiac complex.

The pulse generator 140 further includes a microprocessor coupled to theprogramming circuit, the electrogram analysis circuit and an electricalenergy source (not shown). The microprocessor receives the parametervalues for the electrical pulse from the programming circuit. Cardiaccomplexes in the sensed cardiac signal are also provided to themicroprocessor from the electrogram analysis circuit. The microprocessorthen uses this information to control an energy source to produce theelectrical energy pulse having the parameter values when a predeterminedportion of a cardiac complex occurs in the cardiac signal. In oneembodiment, the microprocessor controls the energy source to generatethe electrical energy pulse for the intravascular stent when thepredetermined portion of a cardiac complex occurs in the cardiac signal.

In one embodiment, the energy source supplies electrical energy and iscoupled to a transducer which converts electrical energy to radiofrequency energy. Radio frequency energy is then produced and can besubsequently delivered to the intravascular stent when the predeterminedportion of a cardiac complex occurs in the cardiac signal. In analternative embodiment, the energy source supplies electrical energy toone or more electrical capacitors operatively coupled to the energysource, microprocessor and the first and second input/output sockets 150and 152. Upon charging the electrical capacitors to a sufficient energylevel, the microcontroller controls the discharge of the electricalcapacitors to produce an electrical energy pulse for the intravascularstent.

In one embodiment, the present subject matter is used to deliverelectrical energy to an intravascular stent implanted in an artery.Procedures and locations for implanting intravascular stent are known inthe art. Once a stent has been implanted in an artery, the cardiac cellsadjacent the intravascular stent are altered by providing electricalenergy in the region surrounding the stent. In one embodiment, theelectrical energy is provided to the region surrounding the stent bydischarging electrical energy between the first electrode and the secondelectrode, where the first electrode is positioned within the arteryproximate the implanted stent and the second electrode is positioned ata location that is set apart, or remote, from the first electrode topermit electrical energy to be delivered between the first and secondelectrodes during a predetermined portion of the cardiac cycle.

In one embodiment, cardiac complexes are sensed by the pulse generator140 using the first electrode 104 and the second electrode 112. Thesensed cardiac complexes are then used to coordinate the production ofthe electrical energy for the stent 102. In one embodiment, theelectrogram signals are used by the pulse generator 140 to deliver theelectrical energy during the predetermined portion of the sensed cardiaccomplexes. For example, electrical energy is coordinated to occur duringa sensed QRS-complex of the cardiac cycle. Alternatively, the electricalenergy is delivered outside the occurrence of the T-wave of the cardiaccycle in a manner that avoids creation of cardiac arrhythmias.

Referring now to FIG. 2, there is shown a block diagram of oneembodiment of the pulse generator 140. In one embodiment, the pulsegenerator 140 is a programmable microprocessor based pulse generator.The pulse generator 140 includes a microprocessor 200, an energy source206, energy storage 210, an energy discharge control circuit 216, aprogramming circuit 218, an electrogram analysis circuit 222, and adisplay screen 226, wherein the components are electrically connected bybus 230.

The display screen 226 is coupled to the programming circuit 218 by bus230. In one embodiment, the programming circuit 218 prompts a userthrough the display screen 226 to input parameters values for theelectrical energy pulses to be produced by the pulse generator 140.Parameter values programmable in the pulse generator 140 include, butare not limited to, energy level, voltage, current, number of pulses orshocks to be produced, and duration of each pulse.

Information related to the operation of the electric pulse generator 140is displayed on the display screen 226. In one embodiment, parametervalues and operational commands for the pulse generator 140 are enteredthrough a data input device 234. In one embodiment, the data inputdevice is a keyboard as shown in FIG. 1. The data input device 234 isinteractively coupled to the programming circuit 218. Alternatively, theparameter values are provided through the interactive display screen226, where the display screen 226 has touch sensitive screen to allowparameter values to be entered by touching the display screen 226.

In addition to having parameter values entered into the programmingcircuit 218, the pulse generator 140 can be used to calculate impedancevalues for cardiac tissue region surrounding an implanted stent. In oneembodiment, the impedance measurements are used to calculate appropriatevoltage values for electrical energy pulses generated by the pulsegenerator 140. In one embodiment, the impedance is determined byproducing and delivering a constant current of insufficient magnitude toeffect heart contraction from the energy source 206 under the control ofthe energy discharge control circuit 216 to the first electrode and thesecond electrode. Alternatively, an alternating current is supplied bythe energy source 206 under the control of the energy discharge controlcircuit 216 to the first electrode and the second electrode.

As the constant current is being delivered across the first and secondelectrodes, the voltage resulting from the delivered current in sensedby the electrodes. From the measured resultant voltage themicroprocessor 200 calculates the impedance of the tissue through whichthe electrical current passed. The impedance value is then used tocalculate a voltage for the electrical energy to be produced by thepulse generator 140. In one embodiment, the electrical energy can thenbe delivered to the stented region of the artery.

In one embodiment, the first lead connector 110 of the catheter 108 andthe second lead connector 116 of the external lead 114 are physicallyand electrically coupled to the pulse generator 140 through the firstinput/output socket 150 and the second input/output socket 152. In oneembodiment, the polarity of electrical energy delivered to the firstinput/output socket 150 and a second input/output socket 152 iscontrolled by energy discharge control circuit 216. In an alternativeembodiment, the polarity of the first and second input/output sockets150 and 152 are fixed as either the cathode terminal or the anodeterminal.

The pulse generator 140 further includes the electrogram analysiscircuit 222. In one embodiment, the electrogram analysis circuit 222analyzes one or more sensed electrocardiogram signals. In oneembodiment, an electrocardiogram signal is sensed between the firstelectrode 104 and the second electrode 112. In an alternativeembodiment, an electrocardiogram signal is sensed between two or moresurface electrodes, where the cardiac signals are provided to the pulsegenerator 140 through electrocardiogram input sockets 240 and 244positioned on the pulse generator 140 and electrically coupled to theelectrogram analysis circuit 222.

As the electrocardiogram signal is sensed, the electrogram analysiscircuit 222 detects the occurrence of QRS-complexes in the signal. Theenergy discharge control circuit 216 operates to cause the energy source206 and/or the energy storage 210 to produce electrical energy duringthe occurrence of QRS-complexes. Alternatively, the electrogram analysiscircuit 222 detects the occurrence of both QRS-complexes and T-waves inthe sensed cardiac signal. The energy discharge control circuit 216 isthen used to ensure the electrical energy is not produced, and thensubsequently delivered, during the occurrence of a T-wave.

In one embodiment, when the pulse generator 140 produces the electricalenergy, the microprocessor 200 commands the energy source 206 to begincharging energy storage 210. In one embodiment, the energy storage 210is one or more capacitors as are known in the art. When the energysource 210 has charged to a sufficient energy level, the energydischarge control circuit 216 is used to produce one or more pulses ofelectrical energy. In one embodiment, the one or more pulses ofelectrical energy can then be delivered to the first and secondinput/output sockets 150 and 152 according to the parameter valuesprogrammed into the pulse generator 140.

In an alternative embodiment, the pulse generator 140 further includes atransducer (not shown), where the energy source 206 supplies electricalenergy and is coupled to the transducer which converts electrical energyto radio frequency energy. The radio frequency energy pulses are thenproduced by the pulse generator 140 for the intravascular stent.

Referring now to FIG. 3, there is shown one embodiment of the catheter108 according to the present subject matter. The catheter 108 includesan elongate body 300 having a peripheral surface 304, proximal anddistal ends 308 and 312. A first electrode 316 is attached on theperipheral surface 304 of the elongate body 300. In one embodiment, thefirst electrode 316 is a coil spring electrode which encircles theperipheral surface 304 of the elongate body 300, where the coil springelectrode has a first end 320 and a second end 324. The coil springelectrode provides the region adjacent the distal end 312 withflexibility while still providing a large electrical discharge surfacearea.

In one embodiment, the length of the first electrode 316 is selected tobe between 80 and 120% of the length of an intravascular stent. In analternative embodiment, the first electrode 316 has a length the rangeof 6 to 40 millimeters. In an additional embodiment, the length of thefirst electrode 316 is selected so that first electrode is positionedproximate the intravascular stent with the first electrode within thelumen of the intravascular stent where the first and second electrodeends are aligned with the first and second ends of the stent,respectively. Alternatively, the first electrodes 316 has a length thatallows for the first electrode 316 to be positioned completely withinthe lumen of the stent, or to be positioned with both the first andsecond ends of the first electrode extending beyond the first and secondends of the stent.

In one embodiment, the first end 320 of the first electrode 316 isspaced longitudinally along the peripheral surface 304 from the distalend 312 by a distance in the range of 2 to 20 millimeters, where 10millimeters is an acceptable distance. It is understood, however, thatthe first end 320 of the first electrode 316 can be located at anynumber of distances from the distal end 312, provided the firstelectrode 316 can still be positioned adjacent the intravascular stent.An electrical lead 332 extends longitudinally within the elongate body300 from a lead connector 330 at the proximal end 308 to electricallyconnect to the first electrode 316.

The catheter 108 also includes a lead pin 334 electrically coupled tothe electrical lead 332, where the lead pin 334 is provided at the leadconnector 330. In one embodiment, the lead connector 330 is releasablyattach to the pulse generator 140 through the first or secondinput/output socket 150 or 152, where lead pin 334 engages a connectorterminal within the input/output socket 150 or 152 to electricallycouple the first electrode to the pulse generator 140.

In one embodiment, the elongate body 300 of the catheter 108 is made ofan extruded polyurethane biocompatible polymer. In an alternativeembodiment, the elongate body 300 of the catheter 108 is made of anextruded silicon rubber. Alternatively, the elongate body 300 of thecatheter 108 can be made of any implantable flexible biocompatiblepolymer (e.g., nylon or polyester) The length of the elongated body 300of the catheter 108 between the proximal and distal ends 308 and 312 isin the range of 90 to 150 centimeters. Additionally, the diameter of theelongate body 300 is in the range of 1 to 3 millimeters (3 to 9 French).In one embodiment, the diameter of the elongate body 300 is less thanthe lumenal diameter of the deployed stent.

The electrically conductive lead 332 is constructed of either stainlesssteel, platinum, or alloys such as MP35N. The first electrode 316 ismade of an implantable metal known in the art, such as platinum,titanium, titanium oxide, titanium nitride, carbon, tantalum pentoxide,iridium, or iridium oxide. Other materials suitable for conductor leadsand electrodes are also known in the art and are considered to be withinthe scope of the present subject matter.

The catheter 108 has a guidewire passageway 340 extending longitudinallyin the elongate body 300 from an inlet end 344 located at the distal end312 to a outlet end 348 located along the peripheral surface 304 of theelongate body 300. In an alternative embodiment, the guidewirepassageway 340 extends longitudinally in the elongate body 300 from theinlet end 344 to an outlet end located at the proximal end 308 of theelongate body 300. In one embodiment, the guidewire passageway 340 isadapted to receive a guidewire for guiding the catheter 108 over theguidewire positioned in the artery. In one embodiment, the guidewirelumen in approximately 20 thousandths of an inch in diameter.

The catheter 108 is relatively flexible at the tip in order to trackover the guidewire thus allowing the catheter 108 to advance throughpatient's arteries. In addition, the catheter includes appropriate axialstiffness (or column strength) at the proximal end 308 to allow forappropriate pushability of the catheter. Choices of catheter design,materials and construction techniques are known which can improve thetrackability and the pushability of a catheter intended to be insertedinto the arteries. Furthermore, the coil structure of the firstelectrode 140 allows for improved flexibility and trackability of thecatheter over the guidewire.

Referring now to FIG. 4, there is shown an alternative embodiment of acatheter 400 according to the present subject matter. The catheter 400includes an elongate body 402 having a peripheral surface 404, proximaland distal ends 408 and 412. A first electrode 416 and a third electrode420 are attached on the peripheral surface 404 of the elongate body 402.In one embodiment, the first electrode 416 and the third electrode 420are annular and encircle the peripheral surface 404 of the elongate body402.

In one embodiment, the first electrode 416 and the third electrode 420are spaced apart and spaced longitudinally along the peripheral surface404 by a distance of between 80 to 120% the length of the intravascularstent. In an alternative embodiment, the first and third electrodes 416and 420 are spread apart in the range of 6 to 40 millimeters. Inaddition, the first electrode 416 is spaced longitudinally along theperipheral surface 404 from the distal end 412 by a distance in therange of 2 to 20 millimeters. In one embodiment, the first and thirdelectrodes 416 and 420 are spread apart so the first electrode 416 ispositioned adjacent a first end of the stent and the third electrode 420is positioned adjacent a second end of the stent. It is understood,however, that the first electrode 416 can be located at any number ofdistances from the distal end 412, provided the first electrode 416 andthe third electrode 420 can be positioned adjacent the intravascularstent.

An electrical lead 432 extends longitudinally within the elongate body404 from a lead connector 434 at the proximal end 408 to electricallyconnect the first electrode 416 and the third electrode 420 in common.In one embodiment, a lead pin 436 electrically coupled to the electricallead 432 is provided at the lead connector 434 to allow the firstelectrode 416 and the third electrode 420 to be releasably attached andelectrically coupled to the pulse generator 140 as previously discussed

In one embodiment, the elongate body 402 of the catheter 400 is made ofan extruded polyurethane biocompatible polymer. In an alternativeembodiment, the elongate body 402 of the catheter 400 is made of anextruded silicon rubber biocompatible polymer. Alternatively, theelongate body 402 of the catheter 400 can be made of any implantableflexible biocompatible polymer. The length of the elongated body 402 ofthe catheter 400 between the proximal and distal ends 408 and 412 is inthe range of 90 to 150 centimeters. Finally, the diameter of thecatheter is in the range of 1 to 3 millimeters (3 to 9 French), wherethe diameter of the elongate body is small enough to allow the catheter400 to pass through the lumen of the intravascular stent.

The electrically conductive lead 432 is constructed of either stainlesssteel, platinum, or MP35N. The first and third electrodes 416 and 420are made of an implantable metal known in the art, such as platinum,titanium, titanium oxide, titanium nitride, carbon, tantalum pentoxide,iridium, or iridium oxide. Other materials suitable for conductor leadsand electrodes are also known in the art and are considered to be withinthe scope of the present subject matter.

The catheter 400 has a guidewire passageway 450 extending longitudinallyin the elongate body 404 from an inlet end 454 located at the distal end412 to a outlet end 458 located along the peripheral surface 404 of theelongate body 402. In an alternative embodiment, the guidewirepassageway 450 extends longitudinally in the elongate body 402 from theinlet end 454 to an outlet end located at the proximal end 408 of theelongate body 402. The guidewire passageway 454 is adapted to receive aguidewire for guiding the catheter 400 over the guidewire positioned inthe arteries.

Additionally the catheter 400 is relatively flexible at the tip to trackover the guidewire to allow the catheter 400 to advance throughpatient's arteries. In addition, the catheter 400 includes appropriateaxial stiffness (or column strength) at the proximal end 408 to allowfor appropriate pushability of the catheter. Catheter design. choices,materials and construction techniques are known which can improve thetrackability and the pushability of a catheter intended to be insertedinto the arteries.

In an alternative embodiment, the third electrode 420 is coupled to athird lead conductor housed within the elongate body 402. The third leadconductor is coupled to a lead pin positioned on the lead connector 434.The input/output socket is adapted to receive the lead connector 434 sothat bipolar cardiac signals can be received and bipolar electricalenergy can be provided to the first and third electrodes 416 and 420from the pulse generator 140. In this present embodiment,electrocardiogram signals used in coordinating the production ofelectrical energy pulses (e.g., electrical or radio frequency) aresensed from two or more surface electrocardiogram electrodes, where eachof the two or more surface electrocardiogram electrodes is coupled to alead connector of two or more lead connectors which are connected to thepulse generator 140. In an alternative embodiment, unipolar signals andelectrical energy can be produced and supplied across the electrodes bycoupling the first and third electrodes in common within the pulsegenerator 140.

Referring now to FIG. 5, there is shown a flow diagram of one embodimentof the present subject matter. At 500, at least a portion of a firstelectrode is positioned within a lumen of a stent. In one embodiment,the stent has been implanted within an artery, where the catheter isinserted into the vasculature to align the first and second electrodeends of the first electrode with the first and second stent ends of thestent. At 510, a second electrode is then positioned at a remoteposition relative to the first electrode. In one embodiment, the remoteposition is a portion of skin of the patient in which the firstelectrode has been positioned. At 520, electrical energy is thendelivered between the first electrode and the second electrode.

Referring now to FIG. 6, there is shown a flow diagram of an additionalembodiment of the present subject matter. At 600, after placing anintravascular stent in an artery, the catheter is inserted into thevasculature to position either the first electrode (FIG. 3) or the firstand third electrodes (FIG. 4) in a location proximate the implantedstent. In one embodiment, the electrode is positioned concentricallywithin the lumen formed by the implanted stent. In one embodiment, theends of the electrode (e.g., 320 and 324 of FIG. 3, or 416 and 420 ofFIG. 4) are positioned adjacent to and aligned with the ends of theimplanted stent. In an alternative embodiment, the electrode ispositioned in a vein or artery that is adjacent to the stented artery.The second electrode is then positioned at a remote position relative tothe first electrode at 610. In one embodiment, the remote position isapproximately at the left lateral aspect of the thorax. In analternative embodiment, the remote position is a dermal surface on thetorso. The first and second, or the first, second and third, electrodesare then coupled to the pulse generator. Cardiac signals are thensensed, and electrical energy is delivered between the first electrodeand the second electrode (or the first, second and third electrodes)during a predetermined portion of the cardiac cycle at 620.

Referring now to FIG. 7, there is shown a flow diagram of an additionalembodiment of the present subject matter. At 700, the first electrode ispositioned within an artery proximate an implanted stent. A secondelectrode, as previously described, is positioned at a remote positionrelative to the first electrode to allow for the electrical energy to bedelivered between the first electrode and the second electrode.

At 710, voltage measurements are made for the electrical energy bytaking bipolar impedance measurements across the first and secondelectrodes. To make these measurements, a constant low current shock isprovided through the electrodes. In one embodiment, the constant lowcurrent shock is provided as direct current between the two electrodes.In an alternative embodiment, the current applied between the electrodesis a subthreshold alternating current. In one embodiment, the lowcurrent or subthreshold alternating current is delivered in the range of10 to 50 microamperes. When an alternating current is used, thefrequency of current pulses is delivered in the range of 5 to 50 KHz,where 20 KHz is an appropriate value.

A bipolar measurement of the resultant voltage is made using the firstand second electrodes. Once the resultant voltage has been measured, theimpedance of the stented arterial region is calculated at 720. In oneembodiment, the impedance is determined by using Ohm's law (V=IR) whereR is impedance. Once the impedance has been determined, the voltage ofthe electrical energy required to deliver a specific amount of currentis calculated at 730. In one embodiment, the voltage is calculated byassuming a critical current density. The critical current density is thecurrent density required to effect changes in the cells residing the inthe arterial structure. In one embodiment, the critical current densityis a predetermined value in the range of 1 to 4 amperes/cm². Themeasured impedance and the critical current density are then used tocalculate the voltage of the electrical energy to be delivered acrossthe electrodes.

In one embodiment, the current to the electrode needed to achieve thecurrent density is computed by multiplying the current density by thesurface area of the electrode. This is only an approximate calculationsince the current density along the electrode will be non-uniform. Inone embodiment, an empirically determined correction factor might alsobe included in the equation to assure the critical current density isachieved along the entire electrode or stented region. Once the currentis determined, the voltage is calculated by multiplying current timesthe impedance. Alternatively, the voltage of the electrical energy to bedelivered across the electrodes can be determined by delivering a smallvoltage shock across the electrodes and measuring the resulting current.Based on the resulting current and the current desired to be deliveredto the stented region, a multiplication factor can be calculated bydividing the desired current by the resulting current. The voltage valueof the small shock can then be multiplied by the multiplication factorto determine the voltage of the electrical energy necessary to deliverthe desired current. For example, if electrical energy delivered at 1.0volt results in 10 milliamps of current, and it is desired to deliver 5amps of current, it would then be known that a pulse of electricalenergy having a voltage value of 500 volts would be required.

Once the voltage of the electrical energy has been determined, the pulsegenerator is programmed to deliver the electrical pulses as previouslydescribed and the electrical energy is delivered to the stented arterialregion under the control of the pulse generator as previously describedat 740.

Besides delivering electrical energy pulses to the stented region of theartery, other types of energy can be delivered. For example, an externaldefibrillator can use an RLC circuit to store and discharge energy,rather than a capacitor storage and discharge energy. In an additionalembodiment, a radio frequency generator could also be used to generateenergy to be delivered to the stented region of an artery. In oneembodiment, the radio frequency generator is similar to those known inthe catheter ablation art.

In addition to the embodiment of delivering electrical energy to stentedcoronary arteries, the present subject matter can also be used todeliver electrical energy to stents positioned in peripheral arteries.The problem of restenosis is known to be associated with peripheralstents and the present subject matter can be used in treating theportions of the peripheral vasculature in which a stent has been placed.Portions of the peripheral vasculature in which stents have been placedinclude the legs and the necks of patients. Therefore, the presentsubject matter is not limited to treatment of coronary arteries, butrather can include all regions of the vasculature in which a stent mightbe placed in order to support the structure of the vessel.

Referring now to FIG. 8, there is shown an alternative embodiment of acatheter 1000 according to the present subject matter. The catheter 1000includes an elongate body 1002 having a peripheral surface 1004, aproximal end 1008 and a distal end 1012. The catheter 1000 furtherincludes an angioplasty balloon 1014 (shown in its expanded state)positioned proximal the distal end 1012 of the catheter 1000. Theelongate body 1002 includes a lumen 1016 extending from an inlet port1018 positioned at the proximal end 1008 to an outlet end (not shown)which opens into the interior region of the angioplasty balloon 1014.The inlet and outlet ports are designed to allow fluid to pass underpressure between the inlet and the outlet port for the purpose ofexpanding and contracting the angioplasty balloon 1014. Structures andprocedures for creating and using catheters having angioplasty balloonsare known.

The angioplasty balloon 1014 further includes a peripheral surface 1020.A first electrode 1022 is positioned on the peripheral surface 1020 ofthe angioplasty balloon 1014. In one embodiment, the first electrode1022 is a flexible conductive layer which is coated onto the peripheralsurface 1020 of the balloon 1014. In an alternative embodiment, thefirst electrode 1022 is a matrix of flexible conductive wires which areintegrated into the peripheral surface 1020 of the balloon 1014, whereportions of the wire surfaces are exposed at the peripheral surface1020. The first electrode is coupled to an electrical lead 1030 whichextends longitudinally within the elongate body 1002 from a leadconnector 1032 at the proximal end 1008 to electrically connect to thefirst electrode 1022. In one embodiment, a lead pin 1036 electricallycoupled to the electrical lead 1030 is provided at the lead connector1032 to allow the first electrode 1022 to be releasably attached andelectrically coupled to the pulse generator 140 as previously discussed.

In one embodiment, the catheter 1000 has a stent in its unexpanded statepositioned over the balloon 1014. The stent and the balloon are advancedover the guidewire to position the stent in the lumen of an artery to bedilated. The balloon is then inflated. Inflating the balloon 1014 causesthe structure of the stent to expand radially to contact and engage theinterior surface of the artery. As the balloon is in its inflatedposition, the first electrode 1022 is in physical contact with thestent. When the stent and the first electrode 1022 are in contact, thepulse generator (as previously described) can be used to generate pulsesof electrical energy. In one embodiment, this electrical energy isdelivered between the first electrode 1022 and the second electrode, aspreviously described.

In one embodiment, the first electrode 1022 has a length of between 80to 120% the length of the intravascular stent. In an alternativeembodiment, the first electrode 1022 has a length in the range of 6 to40 millimeters. In one embodiment, the elongate body 1002 of thecatheter 1000 is made of an extruded polyurethane biocompatible polymer.Alternatively, the elongate body 1002 is made from either an extrudednylon or polyester. In addition, the length of the elongated body 1002between the proximal and distal ends 1008 and 1012 is in the range of 90to 150 centimeters. Finally, the diameter of the catheter with theangioplasty balloon uninflated is in the range of 1 to 3 millimeters (3to 9 French).

The electrically conductive lead 1032 is constructed of either stainlesssteel, platinum, or MP35N. The first electrodes 1022 is made of animplantable metal known in the art, such as platinum, titanium, titaniumoxide, titanium nitride, carbon, tantalum pentoxide, iridium, or iridiumoxide. Other materials suitable for conductor leads and electrodes arealso known in the art and are considered to be within the scope of thepresent subject matter.

The catheter 1000 further includes a guidewire passageway (not shown)extending longitudinally in the elongate body 1002 from an inlet end1040 located at the proximal end 1008 to a outlet end 1042 located atthe distal end 1012 of the elongate body 1002. In an alternativeembodiment, the guidewire passageway extends longitudinally through aportion of the elongate body 1002 from the inlet end located along theperipheral surface 1004 of the elongate body 1002 to the outlet endlocated 1042 at the distal end 1012 of the elongate body 1002. Theguidewire passageway is adapted to receive a guidewire for guiding thecatheter 1000 over the guidewire positioned in the arteries.

Additionally the catheter 1000 is relatively flexible at the tip totrack over the guidewire to allow the catheter 1000 to advance throughpatient's arteries. In addition, the catheter 1000 includes appropriateaxial stiffness (or column strength) at the proximal end 1008 to allowfor appropriate pushability of the catheter. Catheter design choices,materials and construction techniques are known which can improve thetrackability and the pushability of a catheter intended to be insertedinto the arteries.

The present subject matter has now been described with reference toseveral embodiments thereof It will be apparent to those skilled in theart that may changes and modifications can be made to the embodimentsdescribed without departing from the scope of the present invention. Forexample, radioopaque markers can be added to the body of the catheter toassist the physician in positioning the electrode adjacent to a stentimplanted in a arterial artery.

We claim:
 1. A system, comprising: an intravascular stent, wherein theintravascular stent is electrically conductive; a first electrodecoupled to a first lead connector; a second electrode coupled to asecond lead connector; a pulse generator, wherein the pulse generatorincludes a programming circuit, a display screen, a data input device, afirst and a second input/output socket, an electrogram analysis circuit,a microprocessor, and an energy source; wherein the programming circuitis coupled to the display screen, where the programming circuit controlsthe display screen to request parameter values for an electrical energypulse; the data input device is coupled to the programming circuit andthe display screen, where the programming circuit receives the parametervalues provided through the data input device; the first lead connectoris releasably coupled to the first input/output socket and the secondlead connector is releasably coupled to the second input/output socket;the electrogram analysis circuit is coupled to the first electrode andthe second electrode coupled through the first and second leadconnectors, where the electrogram analysis circuit receives a cardiacsignal sensed between the first and second electrode, and where theelectrogram analysis circuit detects cardiac complexes in the sensedcardiac signal; the microprocessor is coupled to the programmingcircuit, the electrogram analysis circuit and the energy source, wherethe microprocessor receives the parameter values from the programmingcircuit and the cardiac complexes in the sensed cardiac signal from theelectrogram analysis circuit, and controls the energy source to generatethe electrical energy pulse having the parameter values for theintravascular stent when a predetermined portion of a cardiac complexoccurs in the cardiac signal.
 2. The system of claim 1, including acatheter, where the catheter includes an elongate body having aperipheral surface, proximal end, and a distal end, where the firstelectrode is positioned on the peripheral surface of the catheterbetween the proximal end and the distal end, and where the first leadconnector is located at the proximal end and a first lead conductorcontained within the elongate body couples the first electrode to thefirst lead connector.
 3. The system of claim 2, wherein a thirdelectrode is positioned on the peripheral surface of the catheter, wherethe first electrode and the third electrode are spaced apart and spacedlongitudinally along the peripheral surface, where the third electrodeis coupled to the first lead conductor contained within the elongatebody.
 4. The system of claim 2, including an external lead, where theexternal lead includes an elongate body having a peripheral surface,proximal end, and a distal end, where the second electrode is positionedat the distal end of the external lead, and where the second leadconnector is located at the proximal end and a second lead conductorcontained within the elongate body couples the second electrode to thesecond lead connector.
 5. The system of claim 1, wherein theintravascular stent has a predetermined length, and wherein the firstelectrode has a length between 80 and 120% of the predetermined lengthof the intravascular stent.
 6. The system of claim 1, wherein the energysource supplies electrical energy and is coupled to a transducer whichconverts electrical energy to radio frequency energy, where the energysource produces a radio frequency energy pulse for the intravascularstent.
 7. The system of claim 1, wherein the energy source produces anelectrical energy pulse for the intravascular stent.
 8. A system,comprising: an intravascular stent, the intravascular stent beingelectrically conductive; a first electrode coupled to a first leadconnector; a second electrode coupled to a second lead connector; two ormore surface electrocardiogram electrodes, wherein each of the two ormore surface electrocardiogram electrodes is coupled to a lead connectorof two or more lead connectors; a pulse generator, wherein the pulsegenerator includes a programming circuit, a display screen, a data inputdevice, a first and a second input/output socket, an electrogramanalysis circuit, a microprocessor, and an energy source; wherein theprogramming circuit is coupled to the display screen, where theprogramming circuit controls the display screen to request parametervalues for an electrical energy pulse; the data input device is coupledto the programming circuit and the display screen, where the programmingcircuit receives the parameter values provided through the data inputdevice; the first lead connector is releasably coupled to the firstinput/output socket and the second lead connector is releasably coupledto the second input/output socket; the electrogram analysis circuit iscoupled to the two or more surface electrocardiogram electrodes throughthe two or more lead connectors, where the electrogram analysis circuitreceives a cardiac signal sensed between the two or more surfaceelectrocardiogram electrodes, and where the electrogram analysis circuitdetects cardiac complexes in the sensed cardiac signal; themicroprocessor is coupled to the programming circuit, the electrogramanalysis circuit and the energy source, where the microprocessorreceives the parameter values from the programming circuit and thecardiac complexes in the sensed cardiac signal from the electrogramanalysis circuit, and controls the energy source to generate theelectrical energy pulse having the parameter values for theintravascular stent when a predetermined portion of a cardiac complexoccurs in the cardiac signal.
 9. The system of claim 8, including acatheter, where the catheter includes an elongate body having aperipheral surface, proximal end, and a distal end, where the firstelectrode is positioned on the peripheral surface of the catheterbetween the proximal end and the distal end, and where the first leadconnector is located at the proximal end and a first lead conductorcontained within the elongate body couples the first electrode to thefirst lead connector.
 10. The system of claim 9, including an externallead, where the external lead includes an elongate body having aperipheral surface, proximal end, and a distal end, where the secondelectrode is positioned at the distal end of the external lead, andwhere the second lead connector is located at the proximal end and asecond lead conductor contained within the elongate body couples thesecond electrode to the second lead connector.
 11. The system of claim9, wherein a third electrode is positioned on the peripheral surface ofthe catheter, where the first electrode and the third electrode arespaced apart and spaced longitudinally along the peripheral surface, andwherein the third electrode is coupled to a third lead connector locatedat the proximal end and a third lead conductor contained within theelongate body couples the third electrode to the third lead connector.12. The system of claim 8, wherein the intravascular stent has apredetermined length, and wherein the first electrode has a lengthbetween 80 and 120% of the predetermined length of the intravascularstent.
 13. The system of claim 8, wherein the energy source supplieselectrical energy and is coupled to a transducer which convertselectrical energy to radio frequency energy, where the energy sourceproduces a radio frequency energy pulse for the intravascular stent. 14.The system of claim 8, wherein the energy source produces an electricalenergy pulse for the intravascular stent.